1. Field of the Invention
This invention relates generally to wireless networks and more particularly to a system and method for granting service on GSM wireless networks.
2. Description of the Background Art
Global System for Mobile Communication (GSM) networks have become widely used in commercial wireless telecommunications systems, such as cellular and Personal Communications System (PCS) systems. FIG. 1 is a prior art block diagram of an exemplary GSM network 100. The GSM network 100 includes a gateway mobile switching center (GMSC) 110, a database 120, and one or more mobile switching centers (MSCs) 130. MSCs 130 have access to visitor's locator registers (VLRs) 140 and control base station systems (BSSs) 150. For example, a MSC 130a has access to a VLR 140a, and the MSC 130a controls BSSs 150a1 and 150a2. In operation, for example, the GSM network 100 may retrieve and update information stored in the database 120 and the VLR 140a to enable a mobile station 160 to communicate with a user of an external network (not shown) via the BSS 150a1, the MSC 130a, and the GMSC 110. The external network may comprise a Public Switched Telephone Network (PSTN), an Integrated Services Digital Network (ISDN), or other external voice and data networks, for example. Alternatively, the GSM network 100 may retrieve and update information stored in the database 120, the VLR 140a, and a VLR 140c to enable the mobile station (MS) 160 to communicate with an MS 170 via the BSS 150a1, the MSC 130a, a MSC 130c, and a BSS 150c1.
BSS 150a1 includes a base station controller (BSC) 180 and one or more base transceiver stations (BTSs) 190, also referred to as base stations (BSs). The BSs 190 are equipped with transceivers, signal processing hardware and software, and antennae 195 for communicating with mobile stations (such as MS 160). A BTS 190a, for example, communicates with the mobile stations located within a cell (or sector or other portion thereof) defined by the effective range of the BTS 190a. BSC 180 controls and manages operation of the BTSs 190 via control signals. In addition, BSC 180 routes and/or processes voice and data signals received from the MSC 130a to a BTS 190c that services coverage area in which the MS 160 is located. Similarly, BSC 180 routes voice and data signals received from a BTS 190b, for example, to the MSC 130a for further processing and transmission.
GSM systems use predefined signal level thresholds (camping parameters) to determine whether a mobile station (such as mobile station 160) is allowed to camp on a broadcast control channel associated with a BTS. Setting these thresholds involves consideration of competing factors. Setting the thresholds at relatively high values ensures that all of the MSs allowed to camp on the broadcast control channel will experience good voice call quality. However, doing so will exclude a greater number of MSs from access to the BTS, causing them to roam on competitors' or other non-preferred networks, or to receive a “No Service” notification. If the broadcast control channel signal thresholds are set at lower values, then a larger number of mobile stations may be able to camp on the broadcast control channel, but certain of the mobile stations may experience poor call quality for GSM services requiring relatively high signal strengths, such as voice calls. Typically, commercial GSM systems set the thresholds at appropriate levels to assure good voice call quality, causing the aforementioned problem of excluding access. It is noted that certain GSM services, such as Short Messaging Service (SMS), require significantly lower signal strengths than do voice calls. It would thus be desirable to provide a method and system that allows the GSM system operator to set camping parameters at values that are small enough to allow MSs that only require access to low-signal requirement GSM services to camp on a broadcast control channel, while guarding against poor voice call quality.